The present invention concerns the monoclonal antibody DS6, tumor-associated antigen CA6, and methods of use thereof.
Malignancy-associated changes of tumor cell membrane sialoglycoproteins and sialoglycolipids (gangliosides) have been observed for decades and are implicated in many aspects of the transformed phenotype, including altered adhesive properties and metastatic potential (Bhavanandan, V. P., Furukawa, K., In: A. Rosenberg (ed.), Biology of the Sialic Acids, pp.144-196, Plenum Press, New York (1995)). Altered, re-expressed or over-expressed sialoglycoconjugates, viewed as tumor-associated antigens (TAAs), are being investigated as targets for a variety of antibody-directed cancer therapies. Some examples include monoclonal antibodies (mabs) directed against sTn (TAG-72) in breast cancer therapy (Estava, F. J. and Hayes, D. F. Monoclonal antibody-based therapy of breast cancer. In: M. L. Grossbard (ed.), Monoclonal antibody-based therapy of cancer, pp.309-338, Marcel Dekker, New York (1998)) and mabs to gangliosides such as GD2, GD3 and GM2 in the therapy of lung cancer and melanoma (Butler, M. O. and Haluska, F. G., In: M. L. Grossbard (ed.), Monoclonal antibody-based therapy of cancer, pp. 339-364, Marcel Dekker, New York (1998); Grant, S. C. et al., In: M. L. Grossbard (ed.), Monoclonal antibody-based therapy of cancer, pp. 365-395, Marcel Dekker, New York (1998)). Nevertheless, there remains a need for new ways to detect and treat cancer in patients.
The present invention is based upon the development of murine monoclonal antibody DS6. This antibody immunohistochemically reacts with an antigen, CA6, that is expressed by human serous ovarian carcinomas but not expressed by normal ovarian surface epithelium or mesothelium. The CA6 antigen has a limited distribution in normal adult tissues and is most characteristically detected in fallopian tube epithelium, inner urothelium and type 2 pneumocytes. Pretreatment of tissue sections with either periodic acid or neuraminidase from Vibrio cholerae abolishes immunoreactivity with DS6 indicating that CA6 is a neuraminidase-sensitive and periodic acid-sensitive sialic acid glycoconjugate (xe2x80x9csialoglycotopexe2x80x9d). SDS-polyacrylamide gel electrophoresis of OVCAR5 cell lysates reveals the DS6 epitope to be expressed on an 80 kiloDalton nondisulfide-linked glycoprotein containing N-linked oligosaccharides. Two-dimensional nonequilibrium pH gradient electrophoresis gels indicates an isoelectric point of approximately 6.2-6.5. DS6 immunostaining can be partially diminished by pretreatment of tissue sections with chloroform/methanol, suggesting that DS6 may also be expressed as a glycolipid. Comparison of the immunohistochemical distribution of the CA6 antigen in human serous ovarian adenocarcinomas reveals similarities to that of CA125, however, distinct differences and some complementarity of antigen expression are revealed by double-label, two-color immunohistochemical studies. The DS6-detected CA6 antigen appears distinct from other well-characterized tumor-associated antigens, including MUC1, CA125, and the histo-blood group-related antigens, sLea, sLex and sTn.
A first aspect of the present invention is a monoclonal antibody selected from the group consisting of monoclonal antibody DS6 and monoclonal antibodies that specifically bind to the antigen or epitope bound by monoclonal antibody DS6, and fragments of the foregoing that specifically bind to the antigen or epitope bound by monoclonal antibody DS6.
A second aspect of the present invention is a method of screening for the presence of cancer in a human subject, comprising the steps of: (a) contacting a biological sample taken from said subject with an antibody as described above under conditions permitting said antibody to specifically bind an antigen in the sample to form an antibody-antigen complex; and then (b) determining the amount of antibody-antigen complex in the sample as a measure of the amount of antigen in the sample, wherein an elevated level of the antigen in the sample is associated with the presence of cancer in said subject.
A further aspect of the present invention is a method of treating cancer in a subject in need thereof, comprising, administering to a subject afflicted with cancer a monoclonal antibody as described above in a therapeutically effective amount.
A still further aspect of the present invention is isolated tumor-associated antigen CA6, an about 80 kDa N-linked glycoprotein, reduced or non-reduced, with a PI of about 6.2-6.5, and containing a sialiadase and periodate sensistive epitope called DS6. Such antigen may be isolated by affinity purification with an monoclonal antibody DS6 as described herein.
The foregoing and other objects and aspects of the present invention are explained in detail in the drawings herein and the specification set forth below.